30 CIRCULAR 80 4, U. S. DEPARTMENT OF AGRICULTURE 



Plains are dependent upon adequate range forage at all seasons. The 

 perennial species, which in 1942 produced more herbage and more 

 usable forage on areas that had been conservatively and lightly stocked 

 than on the heavier stocked pasture, are the only ones that can be 

 depended upon to provide forage at all seasons of the year (fig. 11). 



Individual perennial species show in general the same comparisons 

 as the entire group of perennial plants. The lower production both of 

 herbage and usable forage for all perennial species on the heavily 

 stocked area confirms the lower density, smaller size, and shorter 

 height growth of plants already mentioned as evidence that heavy 

 stocking retarded recovery. 



Effects on the Soil 



Heavy stocking removed too much herbage from the range and 

 reduced the accumulation of litter on the soil surface, thereby exposing 

 the soil surface to washing and blowing. Trampling on these barren, 

 unlittered surfaces lossened the topsoil for easy removal by the wind 

 and exposed the roots of the plants. On flat or level sites, some of the 

 most persistent plants survived on pedestals a few inches higher than 

 the surrounding surfaces. 



On slopes in the sandy loam soil type, heavy grazing and trampling 

 loosened the soil and coarser subsoil materials which were moved down 

 the slopes by gravity (fig. 12, A). Under conservative and light 

 stocking there was little evidence of accelerated erosion or soil move- 

 ment due to grazing even on the steepest slopes (fig. 12, B). 



Effects on the Sheep 



Heavy stocking affected the grazing habits of yearling ewes by 

 forcing them to return to areas already too heavily grazed more often 

 than they naturally would have done. This caused extremely heavy 

 use on certain areas because there were fewer favored places to return 

 to in the smaller pasture. Also, with less forage in the heavily stocked 

 area, the yearling ewes necessarily spent considerably more time 

 searching for forage than those on conservatively and lightly stocked 

 range. Seasonal gains in weight averaged 32 and 33 pounds per head 

 on the conservatively and lightly stocked ranges, and 31 pounds on the 

 heavily stocked range. These differences were statistically significant 

 when corrected for age and initial weight of the ewes. 



At the start of the grazing season the yearling ewes weighed from 

 70 to 77 pounds. Carry-over forage, together with a little green 

 growth, was sufficient in all pastures to permit some gain during the 

 first few weeks of each season, beginning in late March. This carry- 

 over was confined to limited areas on the heavily stocked pasture but 

 was available over most of the conservatively and lightly stocked 

 pastures. An apparent loss of weight occurred at shearing time, 

 usually during the third 28-day period, but this was followed by 

 another period of rapid gain (table 10). By midsummer the choice 

 forage was usually gone from the heavily stocked range and the 

 yearling ewes gained less rapidly than earlier. The weight trends for 

 the sheep grazed at the heavy intensity were similar to the trends for 

 the others, but the tendency to lag at a somewhat lighter weight after 

 midseason was noticeable. ^Yeight gains usually continued with 



